In this kind of device, the application of strain gages is conceived as a simple means for the detection of torsional moments in a "U" shaped conduit. One known device as taught by U.S. Pat. No. 4,187,721 is shown in FIG. 1.
In the figure, strain gages 1 and 2 are mounted adjacent to the intersection of inlet leg 3 and base leg 4 and outlet leg 5 and base leg 4 respectively. Strain gages 1 and 2, which may be viewed as variable resistors dependent upon the distortion of the adjacent portion of the "U" shaped conduit are connected with resistors 6 and 7 to form a bridge circuit communicating with a voltage source as indicated, and connected to AC differential amplifier 8. In the case of simple oscillation of the "U" shaped conduit, the resistivity of strain gages 1 and 2 varies equally thereby providing essentially identical inputs to AC differential amplifier 8. However, in the event of distortion due to Coriolis forces, one of strain gages 1 and 2 will increase in resistivity while the other decreases thereby providing different inputs to AC differential amplifier 8 and providing an output in the form of an AC signal proportional in magnitude and sense to the different strains imposed upon strain gages 1 and 2.
The output from AC differential amplifier 8 is directed to synchronous demodulator 9, which, in conjunction with the conduit oscillation signal, provides a DC output proportional in magnitude and sense to the distortion of the "U" shaped conduit as a result of Coriolis forces.
However, it may well be said that no practicability is found in such an embodiment. The reasons are that the output from such a device is extremely small because of the much too small Coriolis force and that the effects of flow vibration and temperature are great because of the strain gage installations directly on the conduit.
Furthermore, even under simple oscillation, the outputs from both strain gages 1 and 2 do not get small enough as a result a cancellation in the AC differential amplifier due to the phase difference between both strain gages 1 and 2.